The paper discusses a new ventilation control strategy based on supply air CO2 concentration for multi-zone HVAC systems. The stagey offers a great opportunity to reduce energy consumption in HVAC systems while providing the required ventilation according to ASHRAE Standard 62.1 2010. The strategy requires a PI/ or PID controller along with a CO2 sensor located in the main supply air duct to control the supply air concentration by adjusting the outdoor air damper. It also includes a control algorithm to dynamically reset the CO2 concentration set point on a proper time interval basis and using the actual zone airflow rates. The strategy is evaluated by simulation on multi-zone office building conditioned by a typical VAV system and under various USA locations. The results show that significant savings could be obtained by implementing the proposed strategy as compared to the design-occupancy ASHRAE Standard 62.1 2012 procedure and this saving depends mainly on actual occupancy profile and building locations.